Antenna system



June 30, 1953 w. R. Buss ANTENNA SYSTEM Filed Feb. 5, l1946 lilium MOTOR AND GEAR TRAIN gime/YM W. RODE-HC BLISS Patented June 30, 1953 UNITED STATES PATENT OFFICE.

ANTENNA SY STEMv Williamv Roderic Bliss, Washington, D. C.

Application February 5, 1946, Serial No. 645,689

(Cl. Z50-33) (Granted-under Title 35, U. S. Code (1952),

Y sec. .266)` 9 Claims.

This invention relates to radio antenna sys.- tems and in particular'to antenna systems which may be tuned for satisfactory operation. over; a Wide frequency range.

In conjunction with radio receivingv andtransfmitting devices* designed for operation at'V any particular frequency over a wide band of` fre.- quencies, a suitable antenna system is necessary. It is not generally practical to design a. broad: band antenna system providing impedance" match to a transmission line over afr'equency range greater than about 10% of the mean frequency unless some method of' returning` the antenna and any impedance matching device associated therewith is provided.

It is therefore an object of the presentinvention to provide a tunable antenna system having a matched impedance to a transmission line over a wide band of .frequencies.

Another object ofVv the present invention is to provide an antenna system having wide irequency range employing. adjustable capacitive top loading to reduce the mechanical length oi the antenna at the low regions of the frequency range and having negligible capacitive loading at the upper regions oi the frequency' range.

Another object oi the present invention is to provide an antenna system for wide band operation in conjunction with a transmission line in which the antenna electrical length and the impedance matching between antenna and transmission linemay be simultaneously adjusted to obtain optimum operation at a selected fre quency.

Other and further objects and features ofV the present invention will become apparent upon a care-ful consideration of the: following detailed description when taken together with the ace companying drawing which illustrates typical features of the invention and the manner in which the invention may be consideredv to` operate.

Fig. 1` shows a sectional view of an antenna system constructed in accordance with the principles of the present invention.

Fig. 2 is a sectional View of the antenna as'- sembly taken-on the line 2;-2- of Fig. l.

With reference now to Fig. Lan antenna assembly is shown which is mounted upon' a supporting and ground plane establishing member I0: Member I'is preferably of conductive-material and in the case of mounting such as, in aircraft` would comprise a portionv or allA of the' metallic shell of the craft. Protruding from an. aperture in ground planet member". Ilsis. an

elongated cylindrical radiatingelement II.. lille menti IIf may be moved longitudinally toialter. its extension beyond the ground plane; member; Ill. The extension. of element. II above the" f groundv plane member I0 is surrounded by a sleeve ll-A of dielectric material, such asi polystyrene. .Sleeve I I-A is in length approximately equal toY the maximum external height to which element Il is extensible. Internally element II is received by a conductive sleeve member I2 and gear train I5 through gears I8, Il. Threads of the lead screw I# engage an internally threaded actuating member I8r which is affixed to element I'I at the lower end thereof. Element II is held from rotational motion by extensions ISL-A-.irom the actuating member I6 which engage longitudinal slots in the internal surface of sleeve I2. Thus rotation of lead-screw` I4 causes inward; or outward motion oi element II.

Surrounding sleeve. I2fis1 an outer conductive sleeve I9. Electrical energy isV delivered to or from they antenna element II through any opening in sleeve I9v by meansoi a coaxial cable having conductors 2G, 2l. 'Within sleeve I9V is an annular conductive disc 22, shown also in Fig. 2,

which is held in. contactwith sleeves I2 and ISIv bymeans of flexible conductive iinger members 23. distance from the ground plane member I0 by means of two lead screws 24, 25r which engage internally threaded fittings 2B, 2'! attached to disc 22. Lead screws `2li, 25 are provided with rotary motion by means of the motor and gear train 28 through. countergears 29, 30, 3-I.

The. cavity section bounded by annular disc 22,*ground mei-ciber Iii, sleeves t9, i2 and ele-.- mentV Il functions as-Y an impedance matching transformer between the external portion of the radiating element II. and the transmission line conductors 20, 2li. The transformation characteristics of this cavity section are altered by motion upy or down (inA Fig. l) of the annular disc 22. By this motionw itis possible to obtain matching at any selectedrfrequency over a wide frequency range.

At the low frequency end.. of an operating frequency rang-e, themechanical length of a quarter Wave radiating element I I is apt to be quite'large. 'Fo minimize this length and still maintain an electrical length equal toV a quarter wavelength of. the operating,v frequency, a.l capactativetop;v

The annular disc 22A is positionable in itsv loading disc 32 of conductive material is employed. At the center of the lower surface of disc 32, a partially cut-away collar 33 of conductive material is attached. Collar 33 is preferably of such an internal diameter as to allow a snug fit upon sleeve I I-A to provide a rigid mounting for disc 32. Extension of the tip of element I I into collar 33 produces capacitive coupling :between disc 32 and element II so that a top loading effect is achieved. This top loading is adjustable and variable in amount by controlling the extent of penetration of the tip of element II into collar 33. To provide gradual addition of the capacitative top loading device as the extension of element II is increased it was found desirable to provide collar 33 with a partiallj7 cut-away lower end section as shown in Fig. 1.

Where the antenna system is installed aboard aircraft or other locations in which the motion of iiuid past the antenna is rapid, it is desirable to enclose the entire external assembly including top loading,r disc 32 in a suitable enclosure or dome 34 which will protect the antenna from the elements and not interfere seriously with the emission or reception of energy by the antenna system.

In certain installations it may be necessary to control the operation of the antenna system from a distant point. Under this condition it may be desirable that the motor and gear train units I5, 2B form a part of a selsyn or other electrical or mechanical transmission system.

In Fig. 2 a section view of the internal mechanism of the antenna is shown as viewed in the direction 2 2 of Fig. 1. All guide numerals are as previously discussed.

From the foregoing discussion it is apparent that considerable modification of the features of the present invention are possible and while the device herein described and the form of apparatus for the operation thereof constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise device and form of apparatus and that changes may be made therein without departing from the scope ofthe invention as dened in the appended claims. y The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A tunable antenna system operable over a wide frequency range comprising; a ground plane member, a rod antenna selectively adjustable in extension above said ground plane member out to a maximum extension position, and a capacitive loadingr member fixedly positioned with respect to said ground plane member to have a portion proximate at least the tip of said antenna at its maximum extension position, said last named member being capacitively coupleable through said portion to said antenna to increase the electrical length of said antenna as the mechanical extension of said antenna above said ground plane member is increased.

2. A tunable antenna system operable over a Wide frequency range, comprising; a ground plane establishing member, an antenna assembly selectively' adjustable in physical length above said ground plane establishing member, means for adjusting the physical length of said antenna assembly out to a maximum extension position as the desired frequency of operation is changed, a capacitative loading device for said antenna assembly fixedly positioned with respect to the ground plane establishing member and having a portion proximate the tip of said antenna at its maximum extension position, said device being capacitively coupleable through said portion to said antenna assembly in a manner providing negligible capacitive top loading for said antenna assembly when the antenna assembly is adjusted for short length and increasing capacitive top loading as the antenna assembly is adjusted for longer length, and a dielectric sleeve enclosing said antenna assembly and supporting said capacitive loading device.

3. A tunable antenna system operable over a wide frequency range comprising; a ground plane establishing member, a rod antenna adjustable in extension above the ground plane member out to a maximum extension position, a load plate iixedly supported above and parallel to the ground plane member to contain the extension axis of said antenna, and conductive means connected to said load plate and having a portion proximate at least the tip of said antenna at its maximum extension position, said conductive means being capacitively coupleable to said antenna in variable degree to produce a progressively increasing capacity between said rod antenna and said load plate with extension of said rod antenna.

4. A tunable antenna system operable over a wide frequency range comprising; a ground plane establishing member, an antenna assembly selectively adjustable in length above said ground plane establishing member out to a maximum extension position, a dielectric sleeve member affixed to said ground plane member and enclosing said antenna assembly, a capacitive loading device fixedly supported by the outer extremity of said sleeve to have a portion proximate at least the tip of said antenna at its maximum extension position, a transmission line connecting to said antenna assembly, impedance matching means interposed between said antenna assembly and said transmission line, and means adjusting said last named means to obtain optimum impedance match at a selected frequency over a wide band of frequencies.

5. A tunable antenna system operable over a wide frequency range comprising; a ground plane establishing member, a rod antenna member aligned perpendicular to said ground plane establishing member and adjustable in extension from a first side of said ground plane establishing member to a maximum extension position, a load plate fixedly supported above and parallel to the ground plane member to contain the extension axis of said rod member, a dielectric sleeve enclosing said rod member for supporting said load plate, conductive means connected to said load plate and having a portion proximate at least the tip of said rod member at its maximum extension position, said conductive means being capacitively coupleable to said rod member in variable degree to produce a progressively increasing capacity between said rod member and said load plate with extension of said rod member above the first side of said ground plane establishing member, a first conductive sleeve member of diameter greater than said rod member and in contact therewith for receiving the extension of said rod member on the second side of said ground plane establishing member, a second conductive sleeve member surrounding said first con- U ductive sleeve member and placed coaxially therewith and conductively connected to said ground plane establishing member, a positionable annular conductive disc placed within said second conductive sleeve member for conductively joining the rst and second sleeve members, an external energy operative device, transmission line means transferring energy between said rst conductive sleeve member and the energy operative device, and means positioning said rod antenna and the annular conductive disc to obtain optimum operation of the rod antenna at a selected frequency.

6. A tunable antenna system operable over a wide frequency range comprising; a ground plane member, a rod antenna adjustable in extension outwards of said ground plane member to a maximum extension position, a capacitive loading member xedly supported outwards of the tip of said antenna at its maximum extension position, and a conductive collar coaxially aligned with said antenna and extending from said loading member inwards of the tip of said antenna at its maximum extension position. said collar having a bore adapted to enclose an increasing antenna portion with increasing antenna extension, said collar thereby capacitively coupling said loading member and said antenna in controllable degree.

'7. A tunable antenna system substantially set forth as in claim 6 in which the collar has a truncated end section inwards of the capacitive loading member.

8. A tunable antenna system operable over a Wide frequency range comprising; a ground plane member, a rod antenna adjustable in extension outwards of said ground plane member to a maximum extension position, a dielectric sleeve mounted on said member and enclosing said antenna, said sleeve extending outwards from said member to an extremity at least flush with the tip of said antenna at its maximum extension position, a capacitive top loading plate aiiixed to the outer extremity of said sleeve, and a conductive collar coaxially aligned with said antenna and extending from said loading member inwards of the tip of said antenna at its maximum extension position, said collar having a bore adapted to enclose an increasing antenna portion with increasing antenna extension, said collar thereby capacitively coupling said loading plate and said antenna in controllable degree.

9. A tunable antenna system substantially set forth as in claim 8 in which the collar has a truncated end section inwards of the top loading plate.

W. RODERIC BLISS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,119,692 Voigt June 7, 1938 2,168,860 Bernadt Aug. 8, 1939 2,239,909 Buschbeck Apr. 29, 1941 2,313,046 Bruce Mar. 9, 1943 2,344,171 Rote Mar. 14, 1944 2,424,598 Willoughby July 29, 1947 

